This document discusses direct shear tests which are used to determine the shear strength of soils. It provides definitions of key terms like shear strength and failure. It explains that shear strength depends on interactions between soil particles and failures occurs when particles slide past each other. It describes the direct shear test procedure which involves applying normal and shear stresses to a soil sample in a shear box to cause failure. The document provides equations to calculate normal stress, shear stress, dry unit weight and void ratio from direct shear test data.

2. o Introduction
o Procedure
o Calculation
o Introduction
o Definitions
Direct shear test
Shear strength in Soils

3. Thestrengthofamaterialisthegreatest
stressitcansustain.
Thesafetyofanygeotechnicalstructureis
dependentonthestrengthofthesoil.
Ifthesoilfailsthestructurefoundedonit
cancollapse.

4. ENGINEERS MUST UNDERSTANDTHE NATURE OF SHEARINGRESISTANCE
IN ORDER TO ANALYZE SOIL STABILITY PROBLEMS SUCH AS;
• BEARING CAPACITY
• SLOPE STABILITY
• LATERAL EARTH PRESSURE ON EARTH-RETAINING STRUCTURES
• PAVEMENT

5. • Theshearstrengthofasoil isitsresistance toshearing stresses.
• It is a measure of the soil resistance to deformation by continuous displacement
ofitsindividual soil particles.
• Shear strength in soils depends primarily on interactions between
particles.
• Shear failure occurs when the stresses between the particles are such that they
slide orroll pasteachother.

6. 1. betweenparticles(stressindependent
component)
Cementationbetweensandgrains
Electrostaticattractionbetweenclayparticles
2. betweenparticles(stressdependent
component)

7. Theshearstrengthparametersofasoil aredetermined inthelab primarilywith
twotypesoftests;
ShearTest
ShearTest

8. • DirectsheartestisQuickandInexpensive
• Shortcomingisthatitfailsthesoilona
designatedplanewhichmaynotbethe
weakestone
• Usedtodeterminetheshearstrengthofboth
cohesiveaswellasnon-cohesivesoils.
• ASTMD3080

9. • Thetestequipmentconsistsofametalboxin
whichthesoilspecimenisplaced.
• Theboxissplithorizontallyintotwohalves.
• Verticalforce(normalstress)isapplied
throughametalplaten
• Shearforceisappliedbymovingonehalfof
thebox relativetotheothertocausefailure
inthesoilspecimen.

11. DigitalDirect/ResidualShearApparatus
Complete withLeverLoadingAssembly.
220-240V50/60Hz1Ph.

15. 1. Measureinnerside ordiameterofshearboxand findthearea
2. Makesuretopandbottomhalves ofshearboxareincontactandfixed together.
3. Weighout150gofsand.
4. Place the soil in three layers in the mold using the funnel. Compact the soil with 20
blowsperlayer.
5. Place cover ontopofsand
6. Place shearboxinmachine.
7. Applynormalforce. Theweightstouseforthethreerunsare iftheload
isapplied througha ,or ,iftheloadisapplied .
Leverarm loading ratio1:10 (2kgweight =20kg)

16. 8.Startthemotorwithselectedspeed(0.1in/min)sothatthe
rateofshearingisataselectedconstantrate
9.Take thehorizontaldisplacementgauge,verticaldisplacementgageandshearload
gagereadings.Recordthereadingsonthedatasheet.
10.Continuetakingreadingsuntilthehorizontalshearload peaksand thenfalls,or
thehorizontaldisplacementreaches 15%ofthediameter.

17. 1. Determine the dry unitweight, d
2. Calculate thevoidratio,e
3. Calculate thenormalstress&shearstress

21. • ASTMD3080
• CE3121: GeotechnicalEngineeringLaboratory
• SoilMechanics–LaboratoryManual,B.M.DAS(Chapter15)
• SoilProperties,Testing,Measurement,andEvaluation,C.Liu,J.Evett
• Civil Engineering-TexasTechUniversity